The present invention relates to mixed lanthanide-magnesium gallates obtained more particularly in the form of monocrystals and having a particular application in the field of microlasers for integrated optics, or telecommunications by optical fibres and in the field of power lasers emitting in the infrared, visible or ultraviolet ranges, making it particularly possible to effect treatments of materials (welding, drilling, marking, surface treatment), photochemical reactions, controlled thermonuclear fusion, or the polarization of atoms of a gas, such as helium. Microlasers can also be used in the medical field for treating the skin or in microsurgery.
Known mixed lanthanide-magnesium oxides are in particular mixed lanthanum-magnesium gallates of the magnetoplumbite type prepared in pulverulent form for the first time by Philips. These manganese-doped gallates have luminescence properties which have in particular been described in an article "Luminescence of Mn.sup.2+ in SrGa.sub.12 O.sub.19, LaMgGa.sub.11 O.sub.19, and BaGa.sub.12 O.sub.19 " published in the journal of solid state chemistry 7, pp 468-473, 1973 by J. Verstegen. These gallates obtained solely in powder form have significant luminescent properties making it possible to use them in displays. However, they have no laser effect.
FR-A-2 205 733 and US-A-4 216 408 also disclose lanthanum-magnesium gallates containing in particular manganese-doped strontium, which also has luminescent properties, but has no laser effect.
Other mixed lanthanide-magnesium oxides are in particular lanthanum-neodymium-magnesium aluminates, called LNA of formula: La.sub.1-x Nd.sub.x MgAl.sub.11 O.sub.19 with 0&lt;x.ltoreq.1 and which are in particular covered by FR-A-2 448 134 and EP-A-0 043 776.
These aluminates obtained in monocrystalline form have laser properties comparable to those of neodymium-doped aluminium and yttrium garnet known under the abbreviation YAG:Nd and neodymium ultraphosphate (NdP.sub.5 O.sub.14) emitting in the infrared.
LNA has two particularly interesting laser emission wavelengths at 1.054 and 1.083 micrometers, covering that of YAG at 1.064 micrometers. Moreover, it also has an emission wavelength range around 1.32 micrometers, which corresponds to the smallest attenuation by silica optical fibres, thus permitting the transmission of maximum information with minimum losses.
However, the efficiency of the laser emission of LNA is low, like that of YAG, so that at present it cannot be used in all applications.